Wireless Access Control and Security Demystified

A tutorial on the fundamentals of designing a wireless access control system

Common barriers in a building can affect RF coverage. In Figure 3 (A and B), the elevator bank with its metal-lined walls has a strong potential to reflect RF signals and cause an area of low signal strength. Consider this during the design process.

Think outside the box! In the example shown in Figures 4A and 4B, 24 doors require access control. At first glance, you might expect to position the PIM to the corner of the two hallways near doors 6 and 7. But that would mean running wire down the horizontal hallway to the IT closet where the access control panel is located. A simpler option is to calculate the distance from corner to corner using the Pythagorean theorem (A2 + B2 = C2). With a hypotenuse of 212 feet to the extreme corners, we verify that we can get full RF coverage for all 24 doors by shooting across the open space between the two legs of the building.

Wireless access control solutions are designed for outdoor applications as well. Unlike indoor applications which are rated at 200 feet, outdoor applications can run up to 1000 feet with their internal antennae. For longer spans, optional gain antennae may be used to bridge distances up to 4000 feet! Whatever the distance, however, direct line of sight is required between PIMs and wireless access points outdoors.

In the example shown in Figures 5A and 5B, we'd like to add card access to two gates and control them from the main building. The wireless solution for gate 2 is pretty straightforward: Install a PIM near the edge of the main building and install a wireless reader interface at the gate. Gate 1 isn't so easy as the tall tree is obstructing the view to the main building. To overcome this, you'll need a repeater. The easiest option is to place the repeater at gate 2, which retransmits signals between the two-door PIM and the wireless reader interface at gate 1. This may seem complicated, but it is a lot simpler and much more cost effective than digging two trenches totaling 1700 feet.

RF Coverage Testing

As a final certification of a wireless system design, it is highly recommended that you use a pre-installation test kit. As shown in Figure 6, this kit includes a PIM-T tester, which is typically placed where you plan to install a PIM, and a hand-held tester you can take from door-to-door to validate RF coverage in the actual facility.

We know RF signals are capable of penetrating brick, concrete, wood, cinderblock, and plasterboard. With the tester, we are eliminating surprises within the walls that could impede the RF signal. For example, some builders intentionally install wire mesh in the wall to shield the room from RF transmissions. The tester identifies these, letting you modify your design and product placement plans before installing wireless devices.

Another good use for the pre-installation test kit is in historical buildings. The adage "They don't build them like the used to" is often quite true. Compared to current building construction methods and materials, historical buildings often have thick walls made of marble, granite, and stone, sometimes over two feet thick. Fortunately, these buildings are already constructed so you can get on site right away and start testing.

After studying blue prints, selecting product and placement, and developing a system plan, and what happens if the pre-installation test fails? Fortunately, there are several options to try.

1) Sometimes it's a matter of inches, where the PIM-T is placed too close to metal objects like ventilation ducts, pipes, or cabinets. Place the PIM-T in a clear zone or adjacent wall to eliminate obstructions and retest.

2) Rotate the PIM-T 90 degrees and retest.

3) There may be other transmitting devices in or around the building under test. With PIM-T's hard coded to channel 15, you can try a standard PIM to retest using an alternate channel.

4) Relocate the PIM closer to the wireless access point.

5) Use an external antenna.

6) Use a gain antenna.

7) Use a repeater.

Benefits of wireless access control solutions include:

  • Reduced installation cost by up to 35 percent or more.
  • Reduced implementation time by up to 90 percent.
  • Reduced disruption to facilities and workplaces.